(1) Field of the Invention
The present invention relates to an absorber of high energy light, particularly laser light, and to a method for absorbing laser light.
(2) Description of the Related Art
A laser beam is a coherent beam of light having a high density and matched phase as opposed to conventional monochromatic light. The special characteristics of laser beams enable application in steadily expanding fields. Various devices utilizing laser light are provided with laser-light absorbers.
Japanese Unexamined Patent Publication (Kokai) No. 54-118848 discloses a laser-beam scanning apparatus. In FIG. 1, which shows an apparatus 4, reference numeral 2 shows a laser beam, 4a an outlet, 5 a vibrating mirror, 6 a shielding plate, 6a an aperture, 7 a radiation fin, 8 an air jet nozzle for cooling the radiator fin, 9 air, 10 a workpiece, D-D' the vibrating direction, and W a hardening width. The shielding plate 6 is made of a metallic member having a high thermal conductivity, for example, a copper plate.
Japanese Unexamined Patent Publication (Kokai) No. 57-47592 discloses a beam shielding device such as shown in FIG. 2. In this beam shielding device, four sheets 11a, 11b define an aperture for passing the laser beam. The surface area of this aperture can be varied by displacing the sheets 11a, 11b. The sheets 11a, 11b are made of a material which can absorb the laser beam. As an example, graphite is mentioned in the publication.
Japanese Unexamined Patent Publication (Kokai) No. 58-30701 is related to an invention for providing a light-absorbing body with an extremely low reflectivity of light, particularly a CO.sub.2 laser. The light-absorbing body disclosed in the above publication is characterized by being mainly composed of glass and an additional component, such as K.sub.2 O or ZnO and exhibits reflectivity lower than that of metal, black alumite, black paint, and brick. FIG. 3 shows an electric-power receptor for measuring the temperature increase due to irradiation of laser light. In FIG. 3, a laser beam 14 is applied on the glass sheet 15, which is in contact with a thermocouple 13 for measuring the temperature increase relative to a low-temperature copper sheet 12.
Japanese Unexamined Patent Publication (Kokai) No. 58-4103 discloses a shielding plate 23 (FIG. 4) for shielding a laser beam 21. The shielding plate 23 is swivelled around an axis 24. When the shielding plate 23 is swivelled around the axis 24 by a certain angle, the laser beam 24 is emitted through an opening 22. The swivelling motion of the shielding plate 23 is limited by a stopper 25. The apparatus 20 is used as a surgical knife. The invention of the above publication is generally related to the structure of the apparatus 20 as summarized above.
Japanese Unexamined Patent Publication (Kokai) No. 59-66032 disclose a piercing device using a laser, such as shown in FIG. 5. In the figure, 31 shows a light-emitting tube constituted by a 40 W metal halide lamp, 31a a central part, 31 ends, 31c a part to be pierced, 32 a chuck for holding one of the ends 31b, 33 a shield, 34 a laser, such as a CO.sub.2, ruby, or YAG laser, and 35 a convex lens. The shield 33 is made of metal, particularly a high melting-point metal, ceramic, silicon or a metal having a reflective coating. The above publication describes the material properties required by a shield plate for low absorptivity and heat resistance.
Laser light is used also for communication, data transmission, precision measurement, and the like. The following properties are required for a laser-light absorber.
(1) A high efficiency of absorption of the laser energy.
(2) A high efficiency of absorption over a broad ranges of the laser wavelength and output when a device emits or receives such laser light.
In this regard, various laser sources, such as He-Ne lasers with low output and CO.sub.2, ruby, and YAG lasers are available. The wavelength broadly varies from 0.2 .mu.m to 1 mm, and the power broadly varies from 10.sup.-4 to 10.sup.12 W. In measuring the power of laser light either thermally or photoelectrically, a single tester cannot be used because of the broad variation of the wavelength and output and, also, various propagation modes of the laser light. In a tester for measuring the power of a laser having a predetermined range of wavelength and the like, and absorber should have a high absorptivity irrespective of the variation in the wavelength and the like.
(3) Resistance to exposure of strong energy over a long time when high-energy laser light is used.
Especially in a cutting or welding device, the power of laser light is increased, so as to enable working of a large-sized article. This means the absorber used in a tester for measuring the power of laser light must also be resistant to exposure of high-energy laser light.
(4) Small dependency of absorptivity upon the wavelength of laser light, especially when the absorber is used for absorption of high-energy laser light.
Particularly, the absorber used in calorimetric measurement of laser power must have such a small dependency. Calorimetric measurement is one of the thermal measurement methods of laser power. In this method, the laser light is absorbed by a receptor of the absorber for conversion to heat, and the laser power is indirectly measured by means of measuring the temperature change in the receptor, the volume or pressure change in the receptor, or the vaporization amount of the material of the receptor. Calorimetric measurement utilizing, temperature change is the most accurate and is broadly use.
(5) Thermal stability and durability.
It is known to improve the above-described properties of copper by vacuum-depositing gold black or platinum black on a copper body or depositing black paint or carbon black on the copper body. Gold-black deposited copper exhibits the most improved properties (1) to (2) and (4) to (5), but has an unsatisfactory property (3), since it can resist only a few watts per cm.sup.2 in area thereof the highest.
It is known to electrolytically plate chromium on a water-cooled copper box. The chromium-plated water-cooled copper box has an improved property (3) over gold-black deposited copper but its property (3) is still unsatisfactory.
No prior art referred herein discloses the properties of flame-sprayed oxide with regard to absorption of laser light.